THE DOCTOR'S WORLD

THE DOCTOR'S WORLD; West Nile and Its Lessons for Doctors

By LAWRENCE K. ALTMAN, M.D.

Published: August 13, 2002

WASHINGTON, Aug. 11—
As West Nile fever spreads through the country, it is giving scientists a rare picture of how a virus carves a new ecological niche in a hemisphere where it has never been seen.

Most infectious diseases were presumably present at the creation -- or gained a foothold long before the first doctors could determine their origins and chart their spread. We know when smallpox was eradicated from the world (in 1980), but when and where did it first appear? When did it begin to spread to wider areas?

Theories abound. But there is no proof because the earliest doctors lacked the knowledge and tools. Even today, scientists debate whether AIDS, which was first diagnosed in 1981, is a new disease or a newly recognized old one. The only certainty is that AIDS has infected people in virtually every country.

West Nile is different. It was first recognized in this hemisphere just three years ago, in New York City (although the possibility that it occurred earlier cannot be excluded). And thanks to the alert work of scientists then, doctors now know a great deal about how it can spread.

Two axioms of medicine are that infectious agents respect no borders and that jet travel is likely to help infectious diseases spread into new areas. Yet the first case of West Nile fever in the Western Hemisphere came as a surprise.

That outbreak produced 62 human cases, 7 fatal. Since then, West Nile virus has spread to mosquitoes, birds, animals and humans in 36 states and the District of Columbia.

And this summer, it attained epidemic status, causing brain infection (encephalitis or meningitis) in at least 145 cases in Alabama, Illinois, Indiana, Louisiana, Mississippi, Texas and the District of Columbia.

The 85 human cases in Louisiana, including 7 deaths, make the state the scene of the country's worst West Nile outbreak ever.

Compared with scourges like AIDS and influenza, the virus poses a relatively small danger to public health. It can cause fatal brain damage in humans, but seldom does. Still, the wide swath that West Nile has cut in just three years illustrates how vulnerable the United States is to imported diseases.

The speed with which the initial cases were detected and control measures instituted are cited as evidence of the significant improvement in the public health response to new and emerging diseases.

If alert veterinarians and practicing physicians had not sought to identify the cause of the deaths of crows and of human encephalitis in New York City in 1999, health officials would probably have included the human cases in the large ''cause undetermined'' category of encephalitis. If West Nile had not been recognized until this year, scientists might have missed the evolving pattern and even concluded that the virus had been here a long time.

Determining the cycles of transmission of the virus among humans, insects, birds and animals is complex, and the maps of those interrelationships are still too sketchy to provide a full understanding of the ecology of West Nile virus in this country. But when scientists knit together the fragmentary information, the charts could be useful for the future.

Already, West Nile has provided some useful, and sometimes painful, information. Most disturbing is the virus's changing face. The frequency of human outbreaks in Europe, the Middle East and this country has risen over the last decade. So, apparently, has the severity of human disease. Also, at 55, the median age of West Nile encephalitis cases in this country this year seems to be a decade lower than in earlier outbreaks.

The strain of West Nile virus spreading in the United States is identical to one that infected geese and humans in Israel, but no one knows how it came here. Large numbers of bird deaths from West Nile disease have occurred concurrently with human cases only in Israel and the United States, said Dr. Lyle R. Petersen, an epidemiologist who specializes in studying insect-borne infections at the Centers for Disease Control and Prevention.

The reasons are unknown, but the phenomenon raises important questions: whether an older strain of the virus may be gaining in virulence, whether it may be a new strain altogether or whether birds in North America are simply more susceptible to West Nile than those in the Eastern Hemisphere.

Knowledge about the West Nile virus dates from 1937, when a healthy 37-year-old woman from Omogo, Uganda, gave blood for a scientific study of sleeping sickness. The virus was identified by injecting her blood into mice, monkeys and other animals at a laboratory in Entebbe, financed by the Rockefeller Foundation in New York City. Dr. K. C. Smithburn and his team that discovered the virus did not know how the woman became infected.

Recognition of the insect's role in spreading West Nile fever came in the 1950's, when the virus was isolated from patients, birds and mosquitoes from sporadic cases, largely in Egypt.

Israeli doctors reported the first epidemics, in 1951. A large outbreak of an illness in the region in 1941 may have been West Nile fever, but documentation is lacking because diagnostic tests were not available. Later outbreaks in Israel involved nursing home patients and soldiers, but West Nile was nearly forgotten there by the end of the 20th century.

Elsewhere, West Nile fever was more of academic than public health interest because most cases were mild and occurred sporadically.